While I agree with Ford that not responding to one email isn't much of an indicator about a BoD member. A clear pattern of not responding is. There have been members of the BoD who have never responded to an email that I have sent (I would estimate that I have sent every BoD member about 6 emails). Those emails were sent during busy times and slow times.
If there is a pattern of not responding to the people that you represent, I firmly believe that you should be booted as soon as possible.
2 Thessalonians 2:15